JP2690147B2 - Exhaust gas purification device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exhaust gas purification device for purifying exhaust gas in an internal combustion engine such as a diesel engine.

[Prior Art] Conventionally, for example, when purifying exhaust gas from a diesel engine, a filter having a catalyst carrier formed in a honeycomb shape by cordierite and a catalyst component carried on the catalyst carrier is provided on the exhaust side of the diesel engine. This filter is used to collect carbon, NOx, HC, etc. in the exhaust gas for oxidative decomposition.

[Problems to be solved by the invention]

However, since the catalyst carrier in the above filters is made of cordierite with a low melting point (1200-1300 ° C), it can function as a filter due to melting loss in the central part where exhaust gas flow tends to become high temperature. Disappear. For this reason, conventionally, only the central portion of the catalyst carrier was formed into a solid state by cordierite without forming it in a honeycomb shape so as not to have a function as a filter in advance.

Therefore, the collection amount of carbon and the like is reduced by the volume of the central portion, and the collection efficiency of carbon and the like with respect to the entire volume of the catalyst carrier is not good.

The present invention has been made in view of the above circumstances, and an object thereof is to be able to increase the collection efficiency with respect to the entire volume of a catalyst carrier, and in turn, to be small and to collect a large amount of exhaust gas. To provide a purification device.

[Means and actions for solving the problem]

In order to achieve the above object, in the present invention, a casing provided with a passage communicating with the exhaust side of an internal combustion engine, and disposed in the passage, formed into a honeycomb shape by cordierite and having a tubular overall shape. The first catalyst carrier and the second catalyst carrier fitted in the hollow portion of the first catalyst carrier and formed in a honeycomb shape by a porous silicon carbide sintered body are provided.

Therefore, a catalyst carrier having a double structure is formed by the first catalyst carrier and the second catalyst carrier, and the central portion of the catalyst carrier having the double structure effectively utilizes the heat resistance of silicon carbide,
It has excellent heat resistance. Further, since the catalyst carrier having the double structure can utilize the whole to exert the collecting function, the collecting efficiency with respect to the entire volume thereof is improved.

Hereinafter, the present invention will be described in detail with reference to the drawings. First
As shown in the figure, the exhaust gas purification device 1 includes a casing 2 made of a metal pipe, and a passage 2a of the casing 2 is connected to an exhaust pipe Ea of the inner edge engine E. In this casing 2, a catalyst carrier main body having a double structure, which is composed of a first contact carrier 3 made of cordierite and a second catalyst carrier 4 made of a porous silicon carbide sintered body, for purifying exhaust gas. 5 are provided. Further, a third catalyst carrier 6 made of a porous silicon carbide sintered body is arranged on the side surface of the catalyst carrier body 5 on the gas discharge side. Further, on the gas discharge side of the third catalyst carrier 6, a ceramic heater 7 for regeneration is attached to the casing 2.

As shown in FIGS. 2, 3 and 4, the first catalyst carrier 3 of the catalyst carrier main body 5 having a double structure is formed of cordierite having a relatively low melting point (1200 to 1300 ° C.) into a honeycomb shape. And has a circular tubular overall shape having a hollow portion 3a in the center. And this first
A large number of gas passage holes 8 extending in parallel to the axial direction are formed in the catalyst carrier 3, and either one of the supply side and the discharge side of each gas passage hole 8 is alternately sealed by cordierite particles 9. . Further, a silica film is formed on the inner wall surface of each gas passage hole 8 of the first catalyst carrier 3, and an oxidation catalyst composed of a platinum group element, another metal element, or an oxide thereof is supported on the silica film. There is.

On the other hand, the second catalyst carrier 4 is formed in a honeycomb shape by a porous silicon carbide sintered body having a high melting point (up to 3000 ° C.) and has a columnar shape, and the hollow portion 3a of the first catalyst carrier 3 is formed. Is fitted to. A large number of gas passage holes 10 extending in parallel to the axial direction are formed in the second catalyst carrier 4, and one of the supply side and the discharge side of each gas passage hole 10 is formed by a small piece 11 of silicon carbide. They are sealed alternately. Further, a silica film is formed on the inner wall surface of each gas passage hole 10 of the second catalyst carrier 4, and an oxidation catalyst composed of a platinum group element, other metal elements and oxides thereof is supported on the silica film. There is.

Incidentally, as shown in FIG. 1, the third catalyst carrier 6 is formed in a honeycomb shape by a porous silicon carbide sintered body having a high melting point (up to 3000 ° C.) like the second catalyst carrier 4. It is formed in a disc shape and is joined to one side surface of the second catalyst carrier 4. A number of gas passage holes extending in parallel to the axial direction are formed in the third catalyst carrier 6 as in the second catalyst carrier 4, and a silica film is formed on the inner wall surface of the gas passage holes. An oxidation catalyst composed of a platinum group element, another metal element, and an oxide thereof is supported on the silica film. The third catalyst carrier 6 is provided in order to prevent the second catalyst carrier 4 from coming out of the first catalyst carrier 3.

Therefore, as shown by the arrows in FIGS. 1 and 2, when the exhaust gas of the internal combustion engine E is introduced into the catalyst carrier body 5 from the supply side of the casing 2, the first and second catalyst carriers 3, 4 are introduced. Carbon (soot), HC, etc. in the exhaust gas are filtered by the wall portions of the gas passage holes 8 and 10, and are oxidized by the oxidation catalyst. Then, the purified exhaust gas is discharged from the catalyst carrier main body 5. Further, the discharged exhaust gas is further filtered by the wall portion of each gas passage of the third catalyst carrier 6, oxidized by the oxidation catalyst, and discharged from the catalyst carrier 6.

When the regeneration treatment of the double-structured catalyst carrier body 5 used as described above is performed, the ceramic heater 7 with the predetermined amount of carbon retained in the catalyst carrier body 5 is retained.
The catalyst body 5 is heated by means of the third catalyst carrier 6. Then, when the temperature of the catalyst carrier main body 5 on the side closer to the ceramic heater 7 reaches a predetermined temperature (300 to 800 ° C.), the supply of secondary air for promoting combustion to the casing 2 is started. Then, by continuing this treatment, carbon in the catalyst carrier main body 5 is burned and the catalyst carrier main body 5 is regenerated.

In the present invention, the first catalyst carrier 3 and the second catalyst carrier 4 form the double-structured catalyst carrier body 5, and the central portion of the double-structured catalyst carrier body 5 is made of silicon carbonate. By effectively utilizing the heat resistance of the second catalyst carrier 4, the heat resistance is excellent. Further, the double-structured catalyst carrier body 5 can exert the function of collecting carbon, NOx, HC, etc. in the exhaust gas by utilizing the whole including the first and second catalyst carriers 3 and 4. Therefore, it is possible to improve the collection efficiency with respect to the entire volume thereof, and it is possible to provide the small-sized exhaust gas purification device 1 having a large collection amount.

In addition, the second catalyst carrier 4 in the central portion of the catalyst carrier body 5 has a very good thermal conductivity due to silicon carbide, while the first catalyst carrier 3 in the outer peripheral portion has a thermal conductivity due to cordierite. It's not good. Therefore, during heating in the regeneration process, the second catalyst carrier 4
The heat radiation from the peripheral portion of the first catalyst carrier 3 is suppressed by the first catalyst carrier 3, and the first catalyst carrier 3 can also function as a heat insulating layer. Therefore, it is possible to suppress heat radiation from the catalyst carrier body 5 and reach a processing temperature at which regeneration is possible in a short time, so that the regeneration treatment can be advanced in a short time, and heat for raising the temperature of regeneration can be obtained. It is also possible to save energy. Further, the temperature difference between both ends of the catalyst carrier body 5 is kept small. Therefore, it is possible to reduce the rate of cracks occurring in the catalyst carrier body 5 due to the partial temperature difference, increase the number of regeneration treatments, and improve the durability.

Next, examples and comparative examples relating to the regeneration treatment of the dual-structured catalyst carrier body 5 will be described.

〔Example〕

The first catalyst carrier 3 made of cordierite has a diameter of 140 mm, the hollow portion 3a has a diameter of 90 mm, a length of 140 mm, and a thermal conductivity of 2.2 Kc.
Al / m.hr. ° C and specific heat of 0.18 Kcal / kg. ° C were used.
The partition wall between the gas passage holes 8 in the catalyst carrier 3 has a thickness of 0.3 mm, and 200 gas passage holes 8 are formed per square inch.

In order to obtain the first catalyst carrier 3, first, a cordierite honeycomb shaped tubular molded body is produced by extrusion molding. Then, the tubular molded body is microwave dried and fired at about 1200 ° C. in an oxidizing atmosphere.

On the other hand, the second catalyst carrier 4 made of a porous silicon carbide sintered body has a diameter of 88 mm, a length of 140 mm and a thermal conductivity of 40 to 70 Kcal / m.
hr. ° C, specific heat 0.23 Kcal / kg. ° C. The thickness of the partition wall between the gas passage holes 10 in the catalyst carrier 4 is
With 0.3 mm, 200 gas passage holes 10 are formed per square in.

In order to obtain the second catalyst carrier 4, first, a honeycomb-shaped cylindrical molded body made of silicon carbide is formed by extrusion molding.
Then, the cylindrical molded body is freeze-dried and baked at about 2200 ° C. in an inert atmosphere.

Then, the second catalyst carrier 4 is fitted into the hollow portion 3a of the first catalyst carrier 3 to obtain the catalyst carrier body 5 having a double structure.

Further, similar to the second catalyst carrier 4, the third catalyst carrier 6 made of a porous silicon carbide sintered body has a diameter of 140 mm and a length of 20 m.
m, thermal conductivity 40 to 70 Kcal / m.hr. ° C, specific heat 0.23 Kcal / kg. ° C. Further, the partition wall between the gas passage holes in the catalyst carrier 6 has a thickness of 0.3 mm, and each gas passage hole is 1 square i.
200 pieces are formed per n.

To obtain the third catalyst carrier 6, the second catalyst carrier 4
Perform the same process as.

Furthermore, as the ceramic heater 7 for the regeneration treatment, 12
One of V-2.5KW was used.

As shown in FIG. 1, the exhaust gas purifying apparatus 1 was connected to an internal combustion engine E, the internal combustion engine E was operated, and carbon in the exhaust gas was collected. During this trapping operation, the pressure in the exhaust pipe Ea is monitored by the control device C via the pressure sensor Ps and the piezoelectric conversion element Pe, and the pressure is kept at a constant value (0.17
The collection operation was continued until it reached Kg / cm ² ). At this time, the flow rate of the exhaust gas was 50 / sec, and the time required to reach the constant pressure was about 40 minutes. When calculating the amount of carbon collected during this period, the volume of the catalyst carrier body 5 was taken as the total amount of the gas passage holes 8 and 10, and the amount of carbon collected was calculated based on the weight change before and after the collection process. . As a result, the amount of trapped carbon was 15 g /.

Next, the controller S closed the switch S to start energizing the ceramic heater 7. 10 minutes after that, the compressor Co is operated and the air supply pipe Ca
Secondary air to the third catalyst carrier 6 and the catalyst carrier body 5 from
It was supplied at a rate of 50 / min.

At the start of the supply of the secondary air, the temperature of the gas intake side end portion suddenly drops at the end of the combustion of carbon, so the time from the start of energization of the ceramic heater 7 to the temperature drop time was defined as the regeneration time. As a result, the reproduction time was 10 minutes.

Further, the above regeneration treatment was repeated until the catalyst carrier body 5 was damaged. Table 1 shows the results.

(Comparative example)

Same size as the example, diameter 140mm, length 170m
In a conventional type exhaust gas purifying apparatus equipped with m cordierite catalyst carrier and a regenerating ceramic heater (12V-2.5KW), the same regenerating process as in the above-mentioned example was performed. Table 1 shows the results.

As is clear from the results of Table 1, in the catalyst carrier of the comparative example, carbon having a smaller trapping amount than that of the combination of the catalyst carrier main body 5 of the example and the third catalyst carrier 6 (1/1 of the example) It takes 3.5 times longer than the regeneration time of the example to burn 3). Therefore, after collecting the same amount of carbon as in the example, the time until it is burned is
It can be predicted that it will increase 10.5 times, and it can be seen that carbon is efficiently burned in the examples. Further, the number of times of regeneration treatment leading to breakage is smaller than that of the example, and it can be seen that the combination of the catalyst carrier main body 5 and the third catalyst carrier 6 of the example has excellent durability. Furthermore, it can be seen that the examples have no melting loss, the comparative examples have melting loss, and the examples have excellent heat resistance. Table 1 Examples Comparative Examples Heater Energization time (min) 10 4 Carbon capture amount (g /) 15 5 Regeneration treatment time (min) 10 35 Regeneration treatment times (times) 20 or more 7 to 8 No melt damage [Deformation example] As shown in FIG. 5, in order to omit the third catalyst carrier 6 in the above-mentioned embodiment, the outer periphery of the second catalyst carrier 4 made of a porous silicon carbide sintered body is formed into an uneven shape. on the other hand,
In order to fit the second catalyst carrier 4, it is possible to form the first catalyst carrier 3 in half and fit the inner circumference of the hollow portion 3a into the irregularities of the second catalyst carrier 4. Molded into uneven shapes. Then, both catalyst carriers 3 and 4 are assembled and the catalyst carrier body 5
May be formed. In this case, not only the same regeneration treatment result as in the above embodiment can be obtained, but also the second catalyst carrier 4 can be prevented from coming out from the first catalyst carrier 3.

〔The invention's effect〕

As described in detail above, according to the present invention, it is possible to increase the collection efficiency with respect to the entire volume of the catalyst carrier,
As a result, it is possible to provide an exhaust gas purifying apparatus that is small in size and has a large amount of traps.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing an exhaust gas purifying apparatus embodying the present invention and its experimental apparatus, FIG. 2 is a sectional view of a catalyst carrier body, FIG. 3 is a front view of the catalyst carrier body, and FIG. First
FIG. 5 is an exploded perspective view of the catalyst carrier and the second catalyst carrier, and FIG. 5 is a partial cross-sectional view of a modified example. 2 ... Casing, 2a ... Passage, 3 ... First catalyst carrier, 3a ... Hollow part, 4 ... Second catalyst carrier.

Claims (1)

(57) [Claims] 1. A casing (2) having a passage (2a) communicating with the exhaust side of an internal combustion engine (E), and a casing (2) arranged in the passage (2a) and formed in a honeycomb shape by cordierite. A first catalyst carrier (3) having an overall tubular shape, and fitted into a hollow portion (3a) of the first catalyst carrier (3),
An exhaust gas purifying apparatus comprising: a second catalyst carrier (4) formed in a honeycomb shape from a porous silicon carbide sintered body.